Create 12.1_PolinomialsSubtract.cs

12.1. Write a method that adds two polynomials. Represent them as arrays of their coefficients as in the example below:
x2 + 5 = 1x2 + 0x + 5 -> { 5 , 0 , 1 }
Extend the program to support also subtraction and multiplication of polynomials.